There is slightly more than a month to go before the popular Blue Man Group is to open a major show in Toronto, and the media blitz to promote the production has begun. But the group remains locked in a bitter struggle with the unions representing actors, musicians, and stagehands, with no end in sight. Blue Man Group has never been a union show, but has usually paid its participants at rates comparable to those required by labor organizations. Organizers say they don’t understand why they can’t coexist with union shows, as they have in so many other cities, but the unions appear dug in, and are ready to call for a boycott of the Toronto production.